Sputtering, referring to vapor deposition of an ion-bombarded target metal to form a thin film on a substrate, is widely used in the electronics industry. Thin-film magnetic recording disks, for example, are advantageously formed by sputtering successive thin-film layers, including an outer magnetic thin film, on a suitable disk-like substrate. Thin-film sputtering may be used in preparing optical recording medium and in semiconductor fabrication, for producing metal conductive layers on a silicon substrate.
The usual sputtering apparatus consists of a front load-in chamber, one or more sputtering stations at which thin-film layers are deposited on a substrate as the substrate passes through the station(s), and a load-out chamber at the opposite end of the apparatus. Housed in each load chamber is a vertically shiftable magazine constructed for holding a plurality of stacked pallets.
In operation, the apparatus, including the two end chambers, is sealed and evacuated, e.g., to a working vacuum of about 10.sup.-7 Torr or less, and the load-in magazine is lowered to place the lowermost pallet on the magazine onto a conveyor which conveys that pallet through the sputtering station(s) and onto the magazine in the load-out chamber. The two magazines are operated to transfer the vertically stacked pallets successively onto the conveyor, in a bottom-to-top direction in the load-in chamber, and in a top-to-bottom direction in the load-out chamber. After all the pallets have been processed, the apparatus is opened, the pallets removed from the load-out chamber, and a series of fresh substrate-supporting pallets stacked on the magazine in the load-in chamber.
Heretofore, loading and unloading the pallets from a plating apparatus of this type has required inserting the pallets individually into the load-in magazine, and similarly removing the processed pallets individually from the load-out magazine. Transferring pallets to and from the apparatus chambers in this manner is relatively time-consuming, and the loading and unloading time can also lead to significant moisture accumulation in the entire system, requiring longer pump-down times to achieve the desired operational vacuum. Typically, the loading, unloading, and pump-down steps require between 1 and 2 hours for an apparatus in which the total sputtering operation cycle is only about 2 hours. That is, the loading and unloading operation can reduce the total operational time of the apparatus by at least about 50%. Given the high cost of sputtering machines, this lost time represents a serious additional cost in lost production and/or additional machine investment.
Another limitation of the above pallet-loading and unloading procedure is that, in sliding the trays into or out of the magazines, frictional contact between the edges of the pallets and the supporting surfaces of the magazines generates metal particles which get drawn into the apparatus during pump down. These particles, when deposited on the substrates during sputtering, seriously compromise the quality of the resulting sputtered medium, usually requiring that the contaminated medium be discarded.